Numerous means have been sought to improve the fuel-efficiency of moving bodies and, especially, moving bluff bodies by reducing their aerodynamic drag. In the field of surface transportation, and particularly in the long-haul trucking industry, even small improvements in fuel efficiency can reduce annual operating costs significantly. It is therefore advantageous in the design of a vehicle to reduce drag forces, thereby increasing the aerodynamic properties and efficiency of the vehicle.
The over-the-highway cargo-hauling tractor-trailer combination is one vehicle that experiences excessive aerodynamic drag. Generally described, tractor-trailer combinations typically include a tractor having a so-called fifth wheel by which a box-like semi-trailer may be attached to the tractor. The shape of the conventional cargo trailer is essentially a rectangular box. The fore and aft vertical surfaces of such trailers are also generally flat rectangular surfaces.
Most large long-haul cargo trailers similar to those described above exhibit less than optimal aerodynamic performance during highway operation. At highway speeds, these conventional trailers develop a substantial amount of turbulent airflow in the region between the axles of the wheel assembles below the trailer box. This turbulence results in significant aerodynamic drag, increasing both fuel consumption and Nitrogen Oxide (NOx) emissions of the tractor.
Existing trailers utilize side skirts to reduce aerodynamic drag and to provide some under-run protection from a side impact. These trailer skirts are generally flat, homogeneous rubber or a plastic material that are fixedly secured to the trailer and are designed to fold or collapse on impact.